Tree Talk

Quaking AspenSleek stands of quaking aspens (Populus tremuloides) grow in Zion’s higher elevationsZions National ParkCourtesy National Park ServiceU.S. Department of the InteriorThe next time you take a walk in the deep woods or even a stroll through a local park, listen closely. You may hear the trees ‘whispering in the wind.’ We use this familiar phrase to describe the soothing sounds of a gentle breeze through the forest canopy; but it may delight and surprise many to know that this figure of speech is now a proven scientific fact. The trees are talking.

They don’t talk like you and I talk, of course. The spoken word is foregone by the plant kingdom, for now. Theirs is a much subtler form of communication. ‘The Wood Wide Web’, as the scientific journal Nature once dubbed it, is the woodland social network. Within it, trees send electric signals coursing through their roots in order to relay important messages to their neighbors.

Travelling at the speed of about a third of an inch every minute, these timber telegrams take quite a while to accomplish such a task; but what this system lacks in speed, it makes up for with complexity. A tree’s roots will often expand through the soil to an area twice the width of its crown, resulting in the ability of a single tree to grasp the roots of and pass messages to multiple far-away friends at once.

In undisturbed soils, these messages can be expedited symbiotically. Subsoil fungal networks, which intertwine with the roots of trees for nourishment sake, can relay messages much more quickly by connecting otherwise distant, unconnected trees to one another. This becomes quite important when the message pertains to danger: an invasion of damaging pests, for instance.

Usually, though, if a tree needs to get a warning out to its neighbors more quickly, it will do so by other means. When trees are attacked, they emit scent compounds through their leaves. These arboreal aromas can be registered by distant parts of the same tree, far-flung trees in the same grove, or, amazingly, even members of the animal kingdom, which trees will summon to their defense. Even more astonishing is that each scent is custom-catered. Trees will identify their attacker by its saliva and emit a corresponding pheromone meant to attract that attacker’s natural predators. Once they are warned of an invading pest, other trees in the grove may respond similarly.

The usefulness of a tree’s ability to communicate with its neighbors goes beyond emergency warnings or the spreading of other important information. Trees have developed a sophisticated redistribution system in which the strongest trees compensate for weaker ones by sharing their surpluses of sugar. In fact, this system is so efficient that, in the end, each individual tree is nourished at the same rate of photosynthesis. This means that every tree in a grove receives the same amount of sugar per leaf in its crown as every other tree, regardless of its own ability to photosynthesize. As it turns out, trees are highly sociable beings. They take responsibility for friends and family members and see to it that their loved ones are well cared for.

Not all groves are created equal, though. These natural behaviors can be inhibited by intensive thinning of wild groves or absent altogether in planted, monocultural forests. However, when granted enough space and time to be itself, even the most artificial forest can ‘return to its roots.’

So, whenever you find yourself following that wooded path into the forest, think of what secret messages might be coursing through the soil or floating invisibly upon the airwaves? Consider these possibilities, and your walks may now be a little more mysterious.